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$minN (expression operator)

Definition

$minN

Returns the n smallest values in an array.

Note

Disambiguation

This page describes $minN when used as an expression, which returns the n minimum values in an array.

You can also use $minN in these other contexts:

$minN (accumulator), which returns an aggregated value based on a variable number of input documents.
$minN (window function), which is used in the $setWindowFields stage to return the minimum n values from documents in a particular window.

Syntax

{ $minN: { n: <expression>, input: <expression> } }

Field	Description
`n`	An expression that evaluates to a positive integer. The integer specifies the number of array elements that `$minN` returns.
`input`	An expression that evaluates to the array from which to return the minimum `n` elements.

Behavior

You cannot specify a value of n less than 1.
$minN filters out null values found in the input array.
If the specified n is greater than or equal to the number of elements in the input array, $minN returns all elements in the input array.
If input resolves to a non-array value, the expression produces an error.
If input contains elements of different types, comparisons across types follow the BSON comparison order.

Example

The examples on this page use data from the sample_mflix dataset. For details on how to load this dataset into your self-managed MongoDB deployment, see Load the Sample Dataset. If you made any modifications to the sample databases, you may need to drop and recreate the databases to run the examples on this page.

The following example uses the $minN operator to return the two alphabetically-first genres for each movie. The results are returned in the new field firstAlphabeticalGenres created by $addFields.

db.movies.aggregate( [
   { $match: { $expr: { $gte: [ { $size: "$genres" }, 3 ] } } },
   {
      $addFields: {
         firstAlphabeticalGenres: { $minN: { n: 2, input: "$genres" } }
      }
   },
   {
      $project: {
         _id: 0,
         title: 1,
         genres: 1,
         firstAlphabeticalGenres: 1
      }
   },
   { $limit: 5 }
] )

[
  {
    title: 'Winsor McCay, the Famous Cartoonist of the N.Y. Herald and His Moving Comics',
    genres: [ 'Animation', 'Short', 'Comedy' ],
    firstAlphabeticalGenres: [ 'Animation', 'Comedy' ]
  },
  {
    title: 'Gertie the Dinosaur',
    genres: [ 'Animation', 'Short', 'Comedy' ],
    firstAlphabeticalGenres: [ 'Animation', 'Comedy' ]
  },
  {
    title: 'Regeneration',
    genres: [ 'Biography', 'Crime', 'Drama' ],
    firstAlphabeticalGenres: [ 'Biography', 'Crime' ]
  },
  {
    title: 'The Poor Little Rich Girl',
    genres: [ 'Comedy', 'Drama', 'Family' ],
    firstAlphabeticalGenres: [ 'Comedy', 'Drama' ]
  },
  {
    title: 'Wild and Woolly',
    genres: [ 'Comedy', 'Western', 'Romance' ],
    firstAlphabeticalGenres: [ 'Comedy', 'Romance' ]
  }
]

The preceding pipeline:

Uses $match to filter for movies that have at least three genres.
Uses $addFields to create a firstAlphabeticalGenres field. $minN with n: 2 returns the two alphabetically-first values from the genres array.
Uses $project to return only the title, genres, and firstAlphabeticalGenres fields.
Uses $limit to return five documents to improve readability.

Back

$minN-array-element

$minMaxScaler